Pneumatic bellow

ABSTRACT

An air spring rolling-lobe flexible member is made of elastomeric material and has at least two layers of intersecting reinforcement filaments. The reinforcement filaments are arranged in an essentially parallel manner to each other at an angle between 40° and 80° to the direction of the periphery of the rolling-lobe flexible member. At least one component quantity of the reinforcement filaments ( 1, 2 ) within one layer exhibits another strength compared to the remaining component quantity thereof.

[0001] The invention relates to an air spring flexible member made ofelastomeric material having at least two mutually crossing layers ofreinforcement cords. The reinforcement cords are inclined at an angle of40° to 80° to the peripheral direction of the flexible member and arearranged essentially parallel to each other within a layer.

[0002] Air springs have been proved advantageous to a large extent, forexample, as vehicle springs, especially for spring mounting of the wheelaxles of trucks and buses. In automobiles, the use of air springs isincreasing significantly because they offer a balanced comfort at highlevel even for vehicle bodies which are of the sporty kind.

[0003] An air spring has layers of reinforcement cords which runparallel and are embedded in rubber. These reinforcement cords are alsoknown as reinforcement layers which take up the forces which arisebecause of the overpressure in the air spring flexible member. Thereinforcement cords are, in general, so-called cord threads whereinseveral individual fibers (filaments) are twisted into a filament-shapedformation. The reinforcement threads preferably comprise full-syntheticfibers which exhibit a high capability of bending, strength and auniform stretching capability. These fibers are made, for example, ofpolyester, polyamide or aramide and can also be made of metal.

[0004] In the usual method for producing air springs, the individualunvulcanized components of the air spring (inner rubber, reinforcementlayers, outer rubber and, if required, wire cores) are wound ormanufactured to an air spring blank and this blank is then vulcanized.In this method, as a rule, rubberized cord fabric layers are used forthe reinforcement layers. The cord fabric comprises a plurality ofparallel cord threads lying one next to the other and lying in the warpdirection. The cord threads are loosely held together at greaterspacings by a few thin threads in the direction of the weft. After animpregnation operation for increasing the adherence of rubber (fabricpreparation), these cord fabrics are rubberized with a suitable rubbermixture, for example, a mixture on the basis of chloroprene rubber and,after the diagonal cutting into the wanted layer number, are so wound onthe blank that the cords of the various layers come to rest crosswise,preferably, at a cord angle of 40° to 80° to the peripheral direction.With the cord angle, and for a given air spring contour, carrying forceand lateral force of the air spring can be influenced.

[0005] Another method for manufacturing air springs is described, forexample, in DE 198 46 852 A1. In this method, cord-reinforced tubularblanks are continuously manufactured by the spiral-formed wrapping of acoated mandrel with reinforcement cords. The tubular blanks compriseseveral layers and these blanks are, for example, tubular rolling-lobeflexible members for air springs. Overlapping regions and abuttingregions are avoided with this method.

[0006] Newer developments of motor vehicles or chassis, especially inthe automobile area, call for increasingly smaller air spring typeshaving correspondingly increasing operating pressures. Especially highrequirements are imposed on the layers of reinforcement cords in orderto withstand these pressures, that is, to realize a highest possiblebursting pressure while at the same time ensuring a high bendingstrength and therefore to ensure a high service life of the air springs.The number of layers may not be too great so that a high flexibility canbe achieved. At the same time, the strength and the filament thicknessof the reinforcement cords must be so selected that the air springachieves a bursting pressure as high as possible. If the spacing of thecords becomes too great, then the danger is present that the rubbermaterial is not sufficiently burst-tight and a point-for-pointdestruction of the air spring in the clear distances between cords couldoccur.

[0007] In DE 44 23 601 C2, an air spring flexible member is describedwhich exhibits a high stand time at high inner pressures and lowroll-off radii in the rolling lobe. This rolling-lobe flexible memberhas, as a reinforcement layer, three rubberized cord fabric layers oneatop the other. The middle cord fabric layer has a layer strength whichcorresponds to the sum of the layer strengths of the first and thirdlayers. The fabric within one and the same layer comprises uniform cordfilaments, that is, the cord filaments are made of the same material andhave identical cord construction.

[0008] The present invention is based on the task of providing an airspring flexible member having an adequate bursting pressure and a highsurface life which can be manufactured simply and cost effectively.

[0009] This task is solved in accordance with the invention in that atleast one component quantity of the reinforcement filaments within alayer exhibit another strength than the remaining component quantity.

[0010] The basic idea of the invention is that, with the use of highstrength reinforcement filaments, the filament spacing within a layercan be varied in dependence upon the required bursting pressure.However, it is to be noted for ever greater spacing, that the strengthof the rubber material becomes a limiting factor for the air pressure inthe air spring starting at a specific spacing between the filaments. Inorder to prevent that the rubber material in the region of the clearspacing between the high strength filaments is destroyedpoint-for-point, reinforcement filaments having a lower strength aredistributed within the layer between the high strength reinforcementfilaments so that these reinforcement filaments of lesser strengthbridge the region of the clear distance between the filaments of higherstrength. The flexibility of the wall of the flexible member and thespring characteristics are not affected by this measure and high standtimes of the air spring are achieved.

[0011] With the introduction of reinforcement filaments of differentstrengths and therefore also a different rupture strain within a layer,the occurring elongation (rated elongation) in the normal loading casecan furthermore shift to higher values compared to the elongation of alayer made of only high strength material. In this way, pressurestresses can be avoided and these pressure stresses can, for example,occur in the region of the rolling lobe in rolling-lobe flexible membersand can contribute especially to the destruction of the rolling-lobeflexible member.

[0012] Air springs with the arrangement of the reinforcement filamentsin accordance with the invention permit an uncomplicated manufacture inthat, for example, cord fabric layers can be used in the conventionalwrapping method wherein the cord filaments have different strengths. Forexample, hybrid fabrics (mixture fabric of different filaments) can beused wherein, in addition to the filaments made of the one material,also filaments of another material are present.

[0013] Likewise, air springs in accordance with the invention can bemanufactured in accordance with a continuous method as described, forexample, in DE 198 46 852 A1. Reinforcement filaments having differentstrengths are supplied by the warp creel to the positioning ring and theguide element. These reinforcement filaments are then placed on thecoated mandrel.

[0014] The materials having a high strength which can be utilized forair springs are often more expensive than materials having lesserstrength. For this reason, and depending upon the required burstingpressure, a portion of the expensive filaments can be replaced byfilaments which are less expensive. The material costs can be optimizedwithout difficulty in the air spring according to the invention.

[0015] The reinforcement filaments having the different strengths can bearranged within the layer in the most varied ways. Thus, i filaments ofone strength can be disposed next to j filaments of another strengthover the periphery of the air spring alternately, wherein: i=1,2,3 . . .and, independently thereof, j=1,2,3 . . . . For example, over the entireperiphery of the air spring, always two filaments of high strength canbe alternately placed next to one filament of lesser strength.Especially preferred is an arrangement wherein i and j assume the value1 so that the reinforcement filaments alternate over the periphery ofthe flexible member and each of the reinforcement filaments of onestrength are arranged next to the reinforcement filaments of the otherstrength. In this way, a very uniform distribution of the filaments isobtained which ensures excellent spring characteristics because stressdifferences in the wall of the flexible member remain low.

[0016] It is, however, also possible that certain regions (for example,half the periphery, exhibit a specific arrangement, for example, onlyfilaments of high strength whereas other regions exhibit a differentarrangement, for example, filaments of high and low strength 1:1 inalternation). With this kind of distribution, one can, for example,manufacture curved air springs.

[0017] The more complicated the arrangement of the filaments havingdifferent strengths, the more suitable are methods for the manufactureof the air spring wherein the filaments of the layer can be individuallysupplied and wound on a coated mandrel. In a simple manner, thesemethods make possible the desired substitution of individual filamentsof a layer with other filaments without it being necessary to make newfabrics or to apply the fabrics precisely cut and fitted.

[0018] The different strengths of the reinforcement filaments can beachieved, for example, by different filament diameters and/or differentcord constructions of the filaments. The cord construction can differ,for example, by the number of the continuous fibers used, the directionof rotation and the number of twists. Different strengths ofreinforcement filaments can also be achieved with the same basicmaterial in that different pretreatment methods are utilized for themanufacture of the reinforcement filaments.

[0019] It is, however, especially advantageous when the differentstrengths of the reinforcement filaments are achieved with the use ofdifferent materials. For different strengths, the filaments can then beconfigured the same in their construction and their diameters so thatthe layers are very uniform in their outer configuration and, duringroll-off operations, for example, no raised regions can lead to changesof the wear behavior or bending behavior.

[0020] For example, individual fibers or cords of polyamide, polyester,aramide or rayon can be used as reinforcement filaments for the airspring.

[0021] According to an advantageous embodiment of the invention, thereinforcement filaments with higher strength are aramide filaments.Aramide filaments combine high strength with high module, excellentdimensional stability and resistance to heat. As aramides, for example,copolymerizates of essentially terephthalic acid and p-phenylenediamine(para-aramide), for example, Kevlar® or Twaron® can be used as well ascopolymerizates of essentially m-phenylenediamine and isophthalic acid(meta-aramide), for example, Nomex®. However, additional monomers canalso be polymerized in the copolymerizates. Accordingly,terpolymerizates of terephthalic acid, p-phenylenediamine and additionalmonomers, for example, Technora® can be used.

[0022] The reinforcement filaments with lesser strength areadvantageously polyamide filaments, for example, nylon or polyesterfilaments. These filaments are cost effective and their strength issufficient for bridging the distances between the filaments of higherstrength.

[0023] Air spring flexible members of the invention can be bellows, halfbellows or rolling-lobe flexible members. The air spring flexiblemembers are also especially suitable for small bending radii, which mustbe run through many times in the roll-off zone in rolling-lobe flexiblemembers. Furthermore, with the arrangement of the reinforcementfilaments of different strengths and therefore also a differentstructure elongation in the wall of the flexible member, one can achievethat the expansion or elongation, which occurs in the case of a load, isgreater in comparison to the elongation when utilizing only highstrength reinforcement filaments. In rolling-lobe flexible members, thedevelopment of pressure stresses in the region of the rolling lobe cantherefore be avoided. These pressure stresses can lead to thedestruction of the air spring flexible member.

[0024] In the following the invention will be explained in greaterdetail with respect to an embodiment in connection with the accompanyingFIGURE without being limited to this example.

[0025] The single FIGURE shows, schematically, an arrangement ofreinforcement filaments in the center region of an air springrolling-lobe flexible member.

[0026] The FIGURE shows how the reinforcing filaments 1, 2, 3, 4 run inan air spring of the invention having two mutually crossingreinforcement layers. These reinforcement filaments 1, 2, 3, 4 arecompletely surrounded by an elastomeric material (not shown in theFIGURE) in the finished air spring. The filaments 1 and 2 form the innerlayer and the filaments 3 and 4 form the outer layer. The filaments 1and 3 are filaments having a higher strength, such as, aramide filamentswhich are arranged within a layer at a spacing A. Between each twoaramide filaments 1, there is a filament 2 of lesser strength, forexample, a filament made of polyamide or polyester and between each twoaramide filaments 3 there is a filament 4 having lower strength, forexample, of polyamide or polyester. In the finished product, thefilaments (2, 4) reinforce the rubber material disposed between thefilaments (1, 3) to a sufficient amount and prevent the point-for-pointdestruction (rupturing of the rubber) in these regions under theoperating pressures which are present. These air springs can, on the onehand, be manufactured in that corresponding hybrid fabric can be used inthe wrapping method and, on the other hand, the air spring can bemanufactured from a continuously produced tubular blank when the airsprings are air springs having a tubular rolling-lobe flexible member.In the production of the tubular blank, the different reinforcementfilaments can be supplied via a warp creel.

1. Air spring flexible member of elastomeric material having at leasttwo mutually crossing layers of reinforcing filaments with thereinforcing filaments being inclined at an angle of 40° to 80° to theperipheral direction of the flexible member and being arrangedessentially parallel to each other within a layer, characterized in thatat least a component quantity of the reinforcement filaments (1, 2)within a layer have another strength than the remaining componentquantity.
 2. Air spring flexible member of claim 1, characterized inthat the reinforcement filaments (1, 2) alternate over the periphery ofthe flexible member and each one of the reinforcement filaments (1) ofthe one strength being arranged next to a reinforcement filament (2) ofthe other strength.
 3. Air spring flexible member of claims 1 or 2,characterized in that the different strengths of the reinforcementfilaments (1, 2) are achieved by utilizing different materials.
 4. Airspring flexible member of at least one of the claims 1 to 3,characterized in that the reinforcement filaments having a higherstrength are aramide filaments (1).
 5. Air spring flexible member of atleast one of the claims 1 to 4, characterized in that the reinforcementfilaments having lesser strength are polyamide filaments or polyesterfilaments (2).
 6. Air spring flexible member of at least one of theclaims 1 to 5, characterized in that the air spring flexible member is arolling-lobe flexible member.